As the performance, operating speed and integration of semiconductor devices increase and as their power consumption decrease, several problems may appear related to the properties of transistors. For example, a short channel effect may arise as the length of the channel of a field effect transistor is decreased. Such short channel effects may lead to problems such as difficulty in adjusting the threshold voltage of the transistor, an increase in leakage current, and the like. A gate insulation layer or metallic gate that has a high dielectric constant and/or a semiconductor on insulator (SOI) semiconductor substrate (instead of a bulk semiconductor substrate) have been used in efforts to mitigate these problems.
To further address these problems, double gate field effect transistors and recess channel array transistors have also been proposed. Recess channel array transistors address the decrease in the length of a channel that naturally occurs as the integration of a device is increased by providing a recess channel trench in the region that is to be the channel of the transistor. This recess channel trench increases the length of the channel. Double gate field effect transistors have a structure in which gates are disposed on both sides of a channel, and thus the electric potential of the channel can be effectively adjusted and, for example, can be applied in Fin field effect transistors (Fin-FET).